® RT8301A 8-CH Constant Current LED Driver for Display Backlight General Description The RT8301A is a 8-CH constant current sink LED drivers with Dynamic Headroom Control (DHC) function. RT8301A can provide well current matching ability, adjustable VSET to choose the suitable dropout voltage across the MOS / BTJ. Beside that, DHC will provide the stable VFB dimming, thus voltage ripple is kept as small even during the dimming. The RT8301A provides four channel constant currents with less than 3% differences in output current value among the 8-CH and ICs respectively. The constant current is adjustable by each channel external resistor (RISET). The LED brightness can also be adjusted via the EN/PWM pin with PWM dimming duty from 1% to 100%. The RT8301A can operate with external components for high current applications. The DHC function generates feedback signal to DC/DC control loop and regulate the output voltage. When RT8301A selects the LED string with the highest forward voltage, and then the COMP is defined according to that particular string. The COMP voltage is then compared with the voltage of VSET to determine the voltage level of VFB, which therefore control the switching of the primary controller. RT8301A's protection features include Short LED Protection (SLP), Open LED Protection (OLP) and Over Temperature Protection (OTP). When any channel triggers protection function, LED will be turned off and the FAULT pin will pull low. The RT8301A is available in SOP-24 package to achieve optimized solution for PCB space. Simplified Application Circuit VOUT COUT 8 x NLEDs DSL11 VCC FAULT RSLP RT8301A VCC RSET1 DSL18 …… Q1 ZD2 SLP CVCC1 SLP VSET VSET RSET2 VCC COMP RCOMP VFB COMP FAULT RFAULT VCC FAULT OUT1 CCOMP DC11 DC18 D1 …… COMP1 M11 …… CS1 PWM Signal EN/PWM OUT8 …… CS8 …… GND RS11 Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8301A-02 April 2013 M18 RS18 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8301A Features Ordering Information Wide Input Supply Voltage Range : 5V to 24V z Adjustable Channel Current z 3% Current Sense Amplifier Input Offset z VCC Under Voltage Lockout z Thermal Shutdown z Adjustable Dynamic Headroom Control (DHC) Function z LED Open/Short Protection z RoHS Compliant and Halogen Free RT8301A z Applications z z z z z Package Type S : SOP-24 Lead Plating System G : Green (Halogen Free and Pb Free) Note : Richtek products are : ` RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. Pin Configurations LCD TV, MNT Display Backlight DC/DC or AC/DC LED Driver Application General Purpose Constant Current Source Architectural and Decorative LED Lighting LED Street Lighting (TOP VIEW) VFB COMP EN/PWM VCC OUT1 CS1 OUT3 CS3 OUT5 CS5 OUT7 CS7 Marking Information RT8301AGS : Product Number RT8301A GSYMDNN YMDNN : Date Code VSET SLP FAULT GND OUT2 CS2 OUT4 CS4 OUT6 CS6 OUT8 CS8 24 2 23 3 22 4 21 5 20 6 19 7 18 8 17 9 16 10 15 11 14 12 13 SOP-24 Functional Pin Description Pin No. Pin Name Pin Function 1 VFB Feedback Signal Output. 2 COMP LED String Voltage Sense. 3 EN/PWM Chip Enable (Active High) and PWM Pulse Dimming Input. 4 VCC Power Supply Input. 5 OUT1 Channel 1 Current Gate Driver Output. 6 CS1 Channel 1 Current Sense Input. 7 OUT3 Channel 3 Current Gate Driver Output. 8 CS3 Channel 3 Current Sense Input. 9 OUT5 Channel 5 Current Gate Driver Output. 10 CS5 Channel 5 Current Sense Input. 11 OUT7 Channel 7 Current Gate Driver Output. 12 CS7 Channel 7 Current Sense Input. 13 CS8 Channel 8 Current Sense Input. 14 OUT8 Channel 8 Current Gate Driver Output. 15 CS6 Channel 6 Current Sense Input. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8301A-02 April 2013 RT8301A Pin No. Pin Name Pin Function 16 OUT6 Channel 6 Current Gate Driver Output. 17 CS4 Channel 4 Current Sense Input. 18 OUT4 Channel 4 Current Gate Driver Output. 19 CS2 Channel 2 Current Sense Input. 20 OUT2 Channel 2 Current Gate Driver Output. 21 GND Power Ground. 22 FAULT Open Drain Output for Fault Detection. 23 SLP Short LED Protection Sense Input. 24 VSET Highest Voltage LED String. Function Block Diagram VCC BandGap Reference UVLO 0.6V + OUT1 - 4V Regulator - VDD + 8 CS1 0.4V + OUT2 - VDD 2.5V SLP CS2 VCC OTP COMP + VSET - + OUT3 - + CS3 …… + Fault Logic …… EN/PWM - OUT8 - VFB DHC GND CS8 FAULT Operation The RT8301A is a 8-CH LED driver integrated with a feedback controller. When EN/PWM is go high and VCC is exceeded the voltage of the UVLO, it will start-up. During the first 256μs, RT8301A will detect which channels are using. If the CS pin < 0.4V, that channel is defined as “USED” channel. Otherwise, the channel is defined as “UN-USED” if CS pin > 0.4V. And the diver of this channel will be turned off after the un-used checking. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8301A-02 April 2013 Then RT8301A will enter the soft-start state, VFB is kept as 3.3V. After that period, RT8301A selects the LED string with the highest forward voltage, and then COMP is defined according to that particular string. The voltage of COMP will further compare with the voltage of VSET and determine the voltage level of VFB. Beside that, the protection function is activated after the fault blanking period. If the LED string is broken or shorted, RT8301A will turn off channels. The internal MOS of the FAULT will be turned-on, users could add an external pullhigh resistor to get this alarm signal. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8301A Timing Diagram VCC EN/PWM Status Fault Blanking ~ 256ms SS Start VFB = 3.3V ~ 128ms Normal Operation IC Reset (Checking Unused CHs) ~ 256µs The Time of Startup Depends on VOUT ILED Figure 1. Power On by EN/PWM Pin Signals VCC EN/PWM Status Shutdown Delay ~ 32ms Shutdown ILED Figure 2. Power Off by EN/PWM Pin Signals Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8301A-02 April 2013 RT8301A Absolute Maximum Ratings z z z z z z z z z z (Note 1) Supply Input Voltage, VCC ---------------------------------------------------------------------------------------------CS1 to CS8 ----------------------------------------------------------------------------------------------------------------SLP, EN/PWM, COMP, VSET ----------------------------------------------------------------------------------------(OUT1 to OUT8), VFB, FAULT ----------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C −0.3V to 30V −0.3V to 7V −0.3V to 16V −0.3V to 16V SOP-24 ---------------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) SOP-24, θJA ---------------------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ---------------------------------------------------------------------------------------------MM (Machine Model) ---------------------------------------------------------------------------------------------------- 1.111W Recommended Operating Conditions z z z 90°C/W 260°C 150°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage, VCC ---------------------------------------------------------------------------------------------- 5V to 24V Junction Temperature Range -------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VCC = 12V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Supply Current IVCCON VEN/PWM = 4V -- 6 -- mA Shutdown Current ISHDN VEN/PWM = 0V -- 20 -- μA Under Voltage Lockout Threshold VUVLO -- 3.7 -- V Under Voltage Lockout Threshold Hysteresis ΔVUVLO -- 500 -- mV Logic-High VIH 2 -- -- Logic-Low VIL -- -- 1 Shutdown Delay tSHDN -- 32 -- ms EN/PWM Sink Current IIH -- -- 2 μA PWM Dimming Frequency fPWM 90 -- 500 Hz 1 -- 100 % 582 600 618 mV -- 2.5 -- % Enable / PWM EN/PWM Input Threshold Voltage PWM Dimming Duty PWM Frequency = 500Hz V Current Sink CSx Reference Voltage VREF VEN/PWM = 4V Channel to Channel Accuracy VMATCH PWM Frequency = 500Hz, Duty = 80% Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8301A-02 April 2013 (Note 5) is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8301A Parameter Symbol Test Conditions Min Typ Max Unit Output Pins Capability OUTx Source Current IGsr 5 10 22 mA OUTx Sink Current IGsk -- 5 -- mA VSET Voltage Range VSET 2 -- 10 V VFB(MAX) VVSET = 2V, VCOMP = 3V -- 3.3 -- V VFB(MIN) VVSET = 3V, VCOMP = 2V -- 12 -- mV VFB Source Current IFBsr VVSET = 2V, VCOMP = 3V , VVFB = 1.5V -- 100 -- μA VFB Sink Current IFBsk VVSET = 3V, VCOMP = 2V, VFB = 1.5V -- 1.8 -- mA VFB Output Voltage Range Protection Short LED Protection VSLP 2.5 -- -- V Current Sink of SLP ISLP -- 100 -- μA Open LED Protection VOLP -- 0.4 -- V Over Temperature Protection TOTP -- 140 -- °C OTP Hysteresis ΔTOTP -- 30 -- °C Reset tRESET -- 256 -- μs Soft-Start tSS (Note 6) -- 128 -- ms Fault Blanking Time tFB (Note 7) -- 256 -- ms Timing Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability. Note 2. θJA is measured at TA = 25°C on a low effective thermal conductivity single-layer test board per JEDEC 51-3. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. CSX should be left floating for unused channel(s). Note 6. During tSS, VFB = 3.3V and the protection function SLP and OLP are disabled. Note 7. The protection function SLP and OLP are disabled. Before the end of tFB. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS8301A-02 April 2013 RT8301A Typical Application Circuit For General Application VOUT COUT 100µF 8 x NLEDs 12V RSET1 100k DSL1 DSL2 DSL3 DSL4 DSL5 DSL6 DSL7 DSL8 ZD1 Q1 DC1 DC2 DC3 DC4 DC5 DC6 DC7 DC8 RT8301A CVCC1 0.1µF FAULT RSLP 30k 4 VCC CVCC2 10µF 24 SLP 23 VCC VSET RSET2 24k RCOMP COMP 90Hz to 500Hz 3 EN/PWM 2 510k OUT1 5 CS1 6 D1 CCOMP 22nF M1 OUT2 20 CS2 19 M2 OUT3 7 CS3 8 VCC RFAULT 300k 22 1 21 FAULT VFB GND M3 OUT4 18 CS4 17 M4 OUT5 9 10 CS5 16 OUT6 15 CS6 11 OUT7 12 CS7 OUT8 14 M5 M6 M7 M8 CS8 13 RS1 4.99 Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8301A-02 April 2013 RS2 4.99 RS3 4.99 RS4 4.99 RS5 4.99 RS6 4.99 RS7 4.99 RS8 4.99 is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 VAC 90V to 265V CCOMP1 22nF CDD1 10µF COMP CDD2 1µF CX1 0.22µF COMP CS GND R7732 VDD GATE R4 10 R2 1M R1 1M RSW1 1k R5 22 D2 D1 C1 3.3nF CSW1 100pF Q2 Q1 CIN 330µF RSW2 0.05 M1 R3 100k TL431 COUT 220µF RS2 1k RS1 8.2k ZD1 60V VREF RCOMP1 CCOMP1 0.22µF 22k PC817 COMP Photo Coupler D3 RSET2 24k RSET1 100k SLP RT8301A 4 VCC 24 VSET CVCC1 1µF ZD2 Q1 6V8S DSL11 510k CCOMP2 22nF COMP1 SLP 23 VCC DC11 COMP 12V D4 RCOMP2 FAULT R SLP 30k FAULT COMP 2 RFAULT 300k 22 FAULT FAULT 5 OUT1 RFB3 51k 1 VFB CS1 6 CVFB1 33nF RFB2 OUT8 14 FPWM 7.5k 3 EN/PWM 90Hz to 500Hz CS8 13 GND 21 VSET RFB1 300k VCC 12V …… CS1 RS3 0.22nF 50 M18 RS18 4.99 …… …… RS11 4.99 M11 …… DC18 …… DSL18 8 x NLEDs RT8301A For Application Using Fly-Back Converter System is a registered trademark of Richtek Technology Corporation. DS8301A-02 April 2013 VIN 24V DS8301A-02 April 2013 CCOMP2 1nF CDC 10µF Chip Enable 5V CSS 0.33µF RCOMP1 82k CCOMP1 27nF CIN2 VIN 1µF 12V RFSW 200k CIN1 120µF EN SS FSW COMP VDC PWMI OOVP FAULT FB GND PGND ISW RT8525 DRV VIN RSW2 0.05 90Hz to 500Hz RFAULT 300k VCC 12V FAULT RSW1 2.7k M1 D1 ROVP2 9.1k ROVP1 430k COUT 220µF RFB2 68k CVCC1 1µF 24 4 CVFB1 33nF 3 1 RSET2 24k FAULT RFAULT 300k 22 RFB1 2M RFB3 VCC 51k VSET RSET1 100k VCC 12V SLP 5 2 CS8 OUT8 SLP Q1 RSLP 30k DSL11 FAULT 13 14 CCOMP3 22nF COMP1 ZD 6V8S VCC 12V COMP DC11 RCOMP2 D2 510k 23 CS1 6 OUT1 GND 21 EN/PWM VFB FAULT COMP VSET VCC RT8301A …… Copyright © 2013 Richtek Technology Corporation. All rights reserved. RS11 4.99 …… …… M11 …… DC18 …… DSL18 RS18 4.99 M18 8 x NLEDs 4 3 1 22 24 CVFB2 33nF FAULT VSET CVCC2 1µF VCC 12V CS1 OUT1 COMP OUT8 GND CS8 21 EN/PWM VFB FAULT VSET SLP RT8301A VCC …… L1 33µH SLP 13 14 6 5 COMP 2 23 COMP1 DC21 DSL21 RS21 4.99 …… …… M21 …… DC28 …… DSL28 RS28 4.99 M28 8 x NLEDs RT8301A For Application Using Multi-Chip Boost Converter System is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8301A Typical Operating Characteristics Supply Current vs. Temperature 7.0 6.5 6.5 Supply Current (mA) Supply Current (mA) Supply Current vs. Input Voltage 7.0 6.0 5.5 5.0 6.0 5.5 5.0 4.5 4.5 VEN/PWM = 4V VEN/PWM = 4V 4.0 4.0 5 9 13 17 21 25 -50 -25 0 50 75 100 125 LEDx Current vs. PWM Duty Cycle 1.8 120 1.6 100 LEDx Current (mA) Threshold Voltage (V) EN/PWM Threshold Voltage vs. Input Voltage V IH 1.4 VIL 1.2 25 Temperature (°C) Input Voltage (V) 1.0 0.8 ILED1 ILED2 ILED3 ILED4 ILED5 ILED6 ILED7 ILED8 80 60 40 20 VEN/PWM = 4V VEN/PWM = 4V, FPWM = 160Hz 0.6 0 5 9 13 17 21 25 0 20 Input Voltage (V) 40 60 80 100 PWM Duty Cycle (%) CSx Reference Voltage vs. Input Voltage LEDx Current vs. Input Voltage 150 0.7 CS1 CS2 CS3 CS4 CS5 CS6 CS7 CS8 0.5 0.4 0.3 LEDx Current (mA) Reference Voltage (V) 0.6 0.2 120 ILED1 ILED2 ILED3 ILED4 ILED5 ILED6 ILED7 ILED8 90 60 30 0.1 VEN/PWM = 4V VEN/PWM = 4V 0 0.0 5 9 13 17 21 Input Voltage (V) Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 25 5 9 13 17 21 25 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. DS8301A-02 April 2013 RT8301A Power On VFB Output Voltage vs. Input Voltage 4.0 Output Voltage (V) VEN/PWM = 4V 3.2 VCC = 12V, ILED1 = 120mA V FB(MAX) VEN/PWM (2V/Div) 2.4 VFB (2V/Div) 1.6 0.8 I LED1 (100mA/Div) V FB(MIN) 0.0 5 9 13 17 21 Time (1ms/Div) 25 Input Voltage (V) Power Off DHC Function VCC = 12V, ILED1 = 120mA VCOMP = VSET = 1.8V, VFB = 2.3V TSHDN = 32ms VEN/PWM (2V/Div) VCOMP (1V/Div) VFB (2V/Div) VSET (1V/Div) VFB (2V/Div) I LED1 (100mA/Div) Time (25ms/Div) Time (10μs/Div) Open Protection Short Protection VCC = 12V, VEN/PWM = 4V, ILED1 = 120mA VEN/PWM (5V/Div) VCS1 (100mV/Div) VEN/PWM (5V/Div) TFB = 256ms TSHDN = 32ms VFB (2V/Div) VCC = 12V, VEN/PWM = 4V, ILED1 = 120mA VSLP (2V/Div) TSS = 128ms I LED1 (100mA/Div) I LED2 (100mA/Div) Time (100ms/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8301A-02 April 2013 Time (250ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8301A Applications Information The RT8301A is an 8-CH LED current source controller. This device can also drive an external N-MOSFET for various applications. The RT8301A regulates the lowest cathode voltage of the LED strings and generates a feedback control signal to a primary controller to regulate the LED current. Each LED channel current is accurately matched and controlled by sensing an external resistor in series with the MOSFET. All channels' LED brightness can be precisely controlled by applying a PWM signal to the EN/PWM pin. The RT8301A also features several protection functions including LED short protection, LED open protection, and over temperature protection. The device is totally turned off by pulling the EN/PWM pin low after 32ms. output voltage with regulate the LED current of the RT8301A. The feedback level of the whole system is defined by the resistive voltage divider (RSET1, RSET2) at the VSET pin. The minimum setting of the VSET pin voltage is according to the following equation : Minimum VVSET = VF + VDS + 0.6 VOUT Where VF = VD1 + VDC1 VCC DC1 COMP D1 …… + VF - COMP 2 COMP1 + VDS - Under Voltage Lockout To prevent abnormal device operation caused by low input voltages, an under voltage lockout is included which shutdown the device at voltages lower than 3.7V. All functions will be turned off in this state. LED Current Setting Figure 3. COMP Circuit where VF (VD1 + VDC1) is the forward voltage of the diodes and VDS is the dropout voltage of the external MOSFET. Besides, it can improve thermal performance of external MOSFET by VSET pin voltage setting. The loop structure keeps the CS pin voltage, VCSx (x = 1 to 8), equal to the reference voltage, VREF. Therefore, by connecting the resistor, RSx (x = 1 to 8) between the CS pin and GND, the LED current can be determined via the value of RSx. The maximum LED current is calculated according to the following equation : V ILEDx = CSx RSx The R1, R2 and R3 selection is shown in below equation : Brightness Control Where VOUT is converter output voltage, VREF is converter reference voltage and typical IFB is 100μA. The connection is shown as the following Figure 4. The RT8301A provides a PWM dimming function. The LED string current sinks are turned on/off by the PWM signals applied at the EN/PWM pin. Thus, the average LED current can be calculated according to the following equation : V Average ILEDx = CS x duty RSx where duty is the duty cycle of the PWM signal. Dynamic Headroom Control Function The Dynamic Headroom Control (DHC) function is used to generate feedback signal to adjust primary converter Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 VOUT(default) = ( R2 + 1) × VREF R1 R2 + VOUT (MAX.) = ( ) × (VREF − 12m) + VOUT(default) R3 VOUT −(MIN.) = ( R2 ) × (VREF − 3.3) + VOUT(default) R3 R3(MIN.) = VFB − VREF IFB,SR(MAX) Output Voltage of Converter (VOUT) R2 R3 Reference Voltage of Converter (VREF) R1 VFB Output Voltage (10m to 3.3V) of RT8301A Figure 4. DHC Function Setting Circuit is a registered trademark of Richtek Technology Corporation. DS8301A-02 April 2013 RT8301A Chip Enable and PWM Dimming Operation Pull the EN/PWM pin low to drive the device into shutdown mode. Drive the EN pin high to turn on the device again. To control LED brightness, the RT8301A can perform dimming function by applying a PWM signal to the EN/ PWM pin. The average LED current is proportional to the PWM signal duty cycle. MOSFET Selection The RT8301A is designed to drive on external N-MOSFET pass element. MOSFET selection criteria include threshold voltage, VGS(TH), maximum continuous drain current, ID, on resistance, RDS(ON). ,maximum drain-tosource voltage, VDS(MAX), and package thermal resistance, θJA. Input Capacitors Selection The input capacitor reduces current spikes from the input supply and minimizes noise injection to the converter. A ceramic capacitor is recommended for the input capacitor due to its high ripple current, high voltage rating and low ESR, which makes them ideal for switching regulator applications. A 10μF capacitance is sufficient for most applications. Nevertheless, a higher or lower value may be used depending on the noise level from the input supply and the input current to the converter. Note that the voltage rating of the input capacitor must be greater than the maximum input voltage. For better voltage filtering, ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable because of their wide voltage and temperature ranges. Diode Selection The reverse voltage rating is important parameters for consideration when making a diode selection. Make sure that the diode's reverse voltage rating exceeds the maximum output voltage. Power On/Off Sequence When converter's output and VCC is already ready. EN/ PWM pulled high will enable the RT8301A, and IC will check channel unused or not in first period (256μs).The unused channel must be floating. The second period is 128ms soft start time, the RT8301A feedback voltage is 3.3V in this period. Then, IC gets into the fault blanking time (32ms) when PWM duty is 100% since fault blanking counter depends on the PWM on period. After the third period, fault function will turn on. About power off sequence, IC will shut down after 32ms when EN/PWM pin is pulled low. The power on/off flow-chart are shown as the following Figure 5. VCC and EN/PWM Power on Start (RESET) Disable that Channel Un-used (Un-used channel must be float.) IC Latched Power Reset YES Status of Channel Is CSx floating ? (256µs) EN/PWM = L TSHDN > 32ms ? Used VFB = 3.3V OLP = SLP = L Start-up Soft-start Function and ILED Turn on (128ms) OLP = SLP = L Fault Blacking Time (256ms) Over Temperature Protection ? Normal Operation FAULT = H Tj > 140 Turn off All Channel FAULT = L YES NO OLP (TF < 20µs) OPEN / SHORT OLP(TF > 20µs) SLP(TF > 2µs) SLP (TF < 2µs) Tj < 110 Auto-recovery NO LED OPEN/SHORT Protection ? VSLP > 2.5V VOLP < 0.4V Turn-off All Channel YES Figure 5. Power On/Off Flow Chart Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8301A-02 April 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT8301A If the CS pin < 0.4V after a fault blanking period, the counter will be triggered when PWM is high. Moreover, there is a 4μs blanking time on every rising part of PWM. When the counter accumulates to 20μs, all channels will be off and latched. The FAULT will be pulled low. The fault state can only be released by pulling the EN/PWM pin low for 32ms. Short Protection If the SLP pin > 2.5V after a fault blanking period, the counter will be triggered when PWM is high. Moreover, there is a 4μs blanking time on every rising part of PWM . When the counter accumulates to 2μs, all channels will be off and latched. The FAULT will be pulled low. The fault state can only be released by pulling the EN/PWM pin for 32ms. The maximum power dissipation at TA = 25°C can be calculated by the following formula : PD(MAX) = (125°C − 25°C) / (90°C/W) = 1.111W for SOP-24 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 6 allow the designer to see the effect of rising ambient temperature on the maximum power dissipation. 1.2 Maximum Power Dissipation (W)1 Open Protection Over Temperature The RT8301A has an Over Temperature Protection (OTP) function to prevent excessive power dissipation from overheating the device. The OTP shuts down switching operation and disables all channels if the junction temperature exceeds 140°C and sends a fault signal. The channels are re-enabled when the junction temperature cools down by approximately 30°C. Thermal Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : PD(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. Single-Layer PCB 1.0 0.8 0.6 0.4 0.2 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 6. Derating Curve of Maximum Power Dissipation Layout Consideration Follow the PCB layout guidelines for optimal performance of the RT8301A. ` Keep the traces of the main current paths as short and wide as possible. ` Put the input capacitor as close as possible to the device pins (VCC and GND). ` The VFB path must be kept away from noise and short enough to connect VREF. ` The drain pad must large enough to reduce thermal on MOSFET. ` In order maintain ILEDx current match, the grounding paths of each RSx should as similar as possible. For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For SOP-24 package, the thermal resistance, θJA, is 90°C/W on a standard JEDEC 51-3 single-layer thermal test board. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation. DS8301A-02 April 2013 RT8301A The VFB path must be kept away from noise and short enough to connect VREF. VREF Reference Voltage OF Converter VOUT OF Converter R2 R1 CVCC capacitor must be placed as close to the IC as possible. RSET1 VFB 0 CCOMP 0 is use to write jump. RCOMP 24 VSET COMP 2 23 SLP EN/PWM 3 22 FAULT VCC 4 21 GND OUT1 5 20 OUT2 CS1 6 19 CS2 OUT3 7 18 OUT4 CS3 8 17 CS4 OUT5 9 16 OUT6 CS5 10 15 CS6 OUT7 11 14 OUT8 CS7 12 13 CS8 RSET2 CVCC 0 0 0 M1 RS1 M3 0 RS3 0 M2 0 RS4 0 M6 RS5 0 M7 0 0 0 M4 M5 0 0 RS2 0 RS6 0 M8 0 RS8 RS7 0 Q1 0 RSLP ZD 0 0 VOUT of Converter In order maintain ILEDx current match, the grounding COUT paths of each RSx should as similar as possible. The drian pad must large enough to reduce thermal on MOSFET. Figure 7. PCB Layout Guide for Single-clad Board Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8301A-02 April 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 15 RT8301A Outline Dimension H A M B J F C I D Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 15.189 15.596 0.598 0.614 B 7.391 7.595 0.291 0.299 C 2.362 2.642 0.093 0.104 D 0.330 0.508 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.229 0.330 0.009 0.013 I 0.102 0.305 0.004 0.012 J 10.008 10.643 0.394 0.419 M 0.381 1.270 0.015 0.050 24–Lead SOP Plastic Package Richtek Technology Corporation 5F, No. 20, Taiyuen Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries. www.richtek.com 16 DS8301A-02 April 2013